High blood cholesterol

High levels of cholesterol in the blood

What is cholesterol?

Cholesterol is a fatty substance that is found throughout the body and circulates in the bloodstream. It is vital to the normal functioning of the body and is an important constituent of body cells. It is an essential ingredient of vital body chemicals such as hormones produced by various glands, eg the thyroid and ovaries. It is also a component of certain chemicals such as bile acids, which help in the natural digestive processes of fat taken in the diet.

However, when the level of cholesterol in the bloodstream is high, it becomes one of the causes of 'furring up' of the arteries of the body (a process more correctly called 'atherosclerosis'). The arteries of most concern are those supplying blood to the heart, the brain and the legs, since these are the ones most likely to cause serious problems for the individual if they become narrowed or blocked.

How is cholesterol formed?

Nearly all of the cholesterol in the body is manufactured by the liver, whilst a small amount is derived from the diet, formed from digesting foods which contain fat. This diet-derived fat is of two types, namely saturated and unsaturated.

The saturated form is found mainly in the following foods:

  • meat and meat products (beef, lamb, pork, suet, lard dripping) derived from animal sources
  • dairy products (milk, butter, cream, cheese)
  • hard margarine and cooking fat
  • cakes, biscuits, puddings and chocolate.

The unsaturated form is found in the following:

  • vegetable oils
  • soft margarine
  • oily fish eg herring, mackerel, tuna, pilchards and sardines.

The more saturated fats that are eaten the higher the blood cholesterol is likely to be, and therefore the higher the risk of developing coronary heart disease (as described later).

Cholesterol is transported around the body in the bloodstream by attachment to specific proteins, called lipoproteins, along with other small chemical substances derived from the breakdown of fat. These substances are known as triglycerides.

There are two main types of lipoproteins, each containing different amounts of protein and cholesterol. These are high-density lipoprotein (HDL), which contains a high amount of protein and a relatively small amount of cholesterol, and low-density lipoprotein (LDL) containing a smaller amount of protein and a high amount of cholesterol. These are the major cholesterol carrying substances in the bloodstream and about 75 per cent of the circulating cholesterol is carried in the form of LDL, whilst HDLs carry about 25 per cent of the circulating cholesterol.

The significance of the different types of cholesterol is that LDL is 'bad' since it tends to carry cholesterol around the body, high levels of which then result in the depositing of fat onto the artery walls as described above. On the other hand, HDL cholesterol is thought to be 'good' because this tends to carry fats from the body to the liver where it is broken down into other substances and is eventually eliminated from the body. Therefore, when cholesterol levels are measured, the doctor sometimes asks for the result to be divided into HDL and LDL fractions to assess a more accurate measurement of the harmful LDL type. However, high cholesterol levels are most likely to consist mainly of the LDL type.

What causes high blood cholesterol?

What constitutes a 'high' cholesterol level varies from person to person and is explored later in this fact sheet but there are a number of causes of abnormally raised cholesterol levels. These are set out below.

An inherited tendency: These are called 'familial hyperlipidaemias' and there are many different types but they all result in the inheritance of abnormally high levels of cholesterol or another group of fats carried in the blood called the triglycerides. Familial hyperlipidaemia is to be suspected in anyone who has a close family history of heart disease such as angina or heart attacks at an early age.

Certain conditions which are often, but not always, associated with high cholesterol levels: These include diabetes, under activity of the thyroid gland, excessive alcohol consumption, kidney failure and certain conditions of the pancreas (the gland in the abdomen involved with the production of insulin). These account for about 10 to 20 per cent of high cholesterol levels and are called secondary hyperlipidaemias, as they are secondary to another condition.

Poor diet: A diet rich in fatty food and carbohydrates such as cakes, biscuits, sweets, etc., is liable to increase the cholesterol level. However, as mentioned at the beginning, diet only plays a moderate part in the overall level of cholesterol in the blood.

Why is high blood cholesterol important?

If cholesterol is present in abnormally high quantities in the circulating blood, the body is unable to process this amount of fat and so excess cholesterol builds up in the body. It may be deposited in various parts of the body, especially on the walls of the arteries where it forms clumps, or plaques. These can severely narrow and eventually block off the blood supply in the arteries. This results in a loss of oxygen and glucose supply to tissues and muscles supplied by these arteries, which can then become damaged.

The most important area where this build up can occur is in the coronary (heart) arteries. These arteries form a network of blood vessels around the heart. If they are narrowed from cholesterol deposition, this causes the heart muscle to become starved of oxygen. Oxygen starvation may occur temporarily during exercise (resulting in angina pain on exertion) or there may be permanent loss of blood supply that results in a heart attack due to heart muscle damage.

A similar problem can occur in the arteries in the legs, where impaired circulation can lead to pain when walking (called intermittent claudication), and if very severe can actually stop the circulation altogether.

The significance of the different types of cholesterol is that LDL is 'bad' since it tends to carry cholesterol around the body, high levels of which then result in the depositing of fat onto the artery walls as described above. On the other hand, HDL cholesterol is thought to be 'good' because this tends to carry fats from the body to the liver where it is broken down into other substances and is eventually eliminated from the body. Therefore, when cholesterol levels are measured, the doctor sometimes asks for the result to be divided into HDL and LDL fractions to assess a more accurate measurement of the harmful LDL type. However, high cholesterol levels are most likely to consist mainly of the LDL type.

There is no doubt that lowering of the blood cholesterol level will reduce the risk of developing coronary heart disease but the lowest cholesterol level which is desirable is, as yet, unknown.

When should it be measured?

There are often no symptoms associated with high cholesterol and there is ongoing debate as to whether routine measurement should form part of the health screening examinations. There are, however, groups at risk who should be screened:

  • patients with a family history of high cholesterol levels in either parent or siblings. The condition is likely to be inherited as mentioned above.
  • patients who have a family history of premature (or early onset) heart disease (heart attacks or angina), or high blood pressure.
  • patients who are very overweight, smokers, or who themselves have suffered heart problems such as angina or heart attacks. Lowering of cholesterol levels is especially important in these people.
  • those who have other medical conditions such as alcohol problems, diabetes, or kidney disease, all of which can be associated with a high blood cholesterol.
  • patients who have received coronary artery bypass surgery or who have had an angioplasty (a procedure to open up the arteries to the heart).
  • people who have outward signs of a high cholesterol. These signs are unusual as most people who have a high cholesterol do not develop these and paradoxically, some people with these signs do not have high cholesterol. These signs include a white rim around the outside of the iris (known as 'arcus') and whitish deposits commonly around the eyelids and occasionally in other parts of the body.

How is it measured?

This involves a simple blood test. It is traditional to ask for the sample to be taken when the patient has fasted for at least 12-14 hours. This is partly because the reading is slightly more accurate when it is performed on a fasting blood sample but also because it is almost always done in conjunction with measurement of the other type of fats carried in the blood, the blood level of which is very much affected by whether the person has just eaten or not. These other fats are called triglycerides, which have a similar effect on the arteries as cholesterol if they are found in increased amounts in the blood.

If the cholesterol level is found to be increased, the test is usually repeated to ensure that the original result was an accurate one. At the same time, the doctor may check for any likely contributory causes for the high cholesterol, such as thyroid failure or diabetes as mentioned above. If it is thought to be helpful, the LDL and HDL fractions may also be requested.

What level of cholesterol requires treatment?

Since the discovery of the significance of raised cholesterol levels in the blood, there has been a lot of controversy surrounding this question and over the years the advice seems to have changed. However, a consensus of opinion is forming which is based on the fact that the cholesterol level has to be seen as only one of several risk factors for heart disease and atherosclerosis. There are now methods of assessing each person's level of risk. This is based on such things as a person's age, their sex, whether or not they smoke, their blood pressure and cholesterol level. Whether or not treatment of the cholesterol level is required is now based on that person's level of risk.

Therefore, an acceptable level of cholesterol for one person will be a level that requires treatment in another person. There is no longer one single cholesterol level above which everyone would need treatment.

The experts in this field advise that the level of cholesterol should be measured. If the level is above five mmol per litre of blood it should be lowered in the following groups of people:

  • diabetics
  • people with a previous history of heart disease such as angina, heart attack(s) or procedures to treat these such as coronary artery bypass surgery or angioplasty (to open up the heart arteries)
  • people who are estimated to have a 30 per cent or greater risk of developing coronary heart disease (angina or heart attacks) over the next 10 years. (In future this may be widened to include those with a 10 year risk of 15 per cent or more, but this would include about 25 per cent of the adult population and this would cost the country a great deal as a greater number of cholesterol lowering drugs would need to be prescribed).

In those people listed above, the level of cholesterol aimed for is below 5 mmol per litre of blood or a reduction of 30 per cent (whichever is greater). There is some discussion amongst specialists as to whether these levels should be even lower in certain groups of people.

What is the treatment for raised cholesterol?

There is a small group of patients whose raised cholesterol level is due to another condition, as mentioned above, such as thyroid gland failure or excessive alcohol intake. In these people, the initial treatment is of the underlying condition, since this will almost always result in a natural return of the cholesterol level to normal.

In those people with primary hypercholesterolaemia (ie high cholesterol which is not the result of another illness), which make up the majority of cases, treatment involves dietary modification and where necessary, tablets to control obesity and reduce the cholesterol level.

Dietary modification: Research has shown that the amount of fat in the diet, and particularly the amount of saturated fat, has a greater effect on the level of cholesterol in the blood than the actual amount of cholesterol in the food someone eats. Therefore there are some foods which, although high in cholesterol, are alright to eat in moderation. These include eggs and prawns both of which are high in cholesterol but low in saturated fat. Seafood also contains healthy fatty acids called omega 3 fatty acids.

Therefore weight reduction and avoidance of saturated fats in the diet are the main factors which will reduce the level of cholesterol in the blood.

The following measures will aid in this:

  • Use skimmed or semi skimmed milk.
  • Grill, bake or steam foods rather than frying.
  • Eat smaller portions of meat and trim off any excess fat.
  • Eat low fat cheeses and margarine and spread margarine and butter thinly.
  • Do not add fat or oil during cooking.
  • Make sure low fat foods are labelled 'low in saturated fat' if a specific low cholesterol diet is required.

Foods high in saturated fats and therefore best avoided or eaten in small amounts include:

  • Fatty cuts of meat, black pudding, salami and sausages.
  • Butter, lard and cream.
  • Hard cheeses.

Food high in unsaturated fats can help to reduce cholesterol levels and include:

  • Oily fish.
  • Vegetable oils.
  • Nuts and seeds.

Medication

This works by lowering the blood cholesterol, the triglyceride level, or both. There is now overwhelming evidence that lowering the blood cholesterol by diet and/or drugs will reduce the chances of patients developing coronary artery disease. Cholesterol lowering tablets are not a substitute for a low fat diet. There are a number of groups of these drugs.

Information Brand Generic Label Rating
Atorvastatin Lipitor Atorvastatin On-Label
Xenical Xenical Orlistat Off-Label

Mevacor (Lovastatin), Pravachol (Pravastatin), Zocor (Simvastatin), Premarin (Conjugated Estrogens)

Last updated 20 May 2012


©2007-2012. Nmihi.com All rights reserved. This site is for information and support only.